1. Field of Invention
The present invention relates to a navigation system.
2. Description of Related Art
In a conventional navigation apparatus for use in a vehicle such as a car, an optimum route from a specified start point to a specified destination is searched for on the basis of road map data. As a result of the search, a detected route is displayed on display means. During the route search, a searching condition is set such that a route with a shortest distance from the specified start point to the specified destination or a route with a shortest driving time is detected.
A conventional system is known that transmits road traffic information to a navigation apparatus installed in a vehicle such that a user (such as a driver) of the vehicle can select a route to avoid traffic congestion indicated by the received road traffic information. For example, in a system called VICS® (Vehicle Information & Communication System), road traffic information indicating congestion on roads or traffic restrictions is produced based on information collected from a traffic control system managed by the police, Japan Highway Public Corporation, or the like. The road traffic information is transmitted to navigation apparatuses via communication means. If a navigation apparatus receives the road traffic information, that navigation apparatus displays congested sections of roads on a map in accordance with the received road traffic information. A conventional information center is also known which processes road traffic information and transmits selected pieces of road traffic information from a server of the information center to navigation apparatuses via communication means such as a portable telephone (a specific description thereof may be found, for example, in Japanese Unexamined Patent Application Publication No. 9-274697).
However, in the conventional systems described above, communication between a navigation apparatus and a server only starts after the navigation apparatus is turned on. Therefore, data is not received from the server and is not displayed on a display means to a user until the navigation apparatus is turned on. Thus, when a user in a vehicle wants to check or use traffic information received from the server before the user starts to drive the vehicle, the user has to wait for traffic information to arrive.
When a user wants to acquire, from a server, road traffic information associated with a route from a current position to a specified destination, the user cannot get or use the road traffic information until the user inputs the destination in the navigation apparatus. Thus, the user has to perform a troublesome operation, which requires additional operation time.